Two fully-oxidized polycrystalline samples were prepared by using a sol-gel technique at an O pressure of 1atm, and were investigated at temperatures ranging from 5 to 100K. Structural changes were determined by means of Rietveld analysis. The O content was found to be equal in both samples, but the unit cell parameters and interatomic bond distances differed significantly. The structural changes, as a function of temperature, showed that the displacements of the apical O atom in single and double CuO chain blocks were different. In agreement with a decreased coherence length along the c-axis, as detected by neutron diffraction, electron diffraction studies revealed appreciable streaking in some samples. High-resolution electron microscopy indicated that the reason for the streaking was the presence of stacking faults in the sequence of single and double CuO chain blocks.

P.Berastegui, P.Fischer, I.Bryntse, L.G.Johansson, A.W.Hewat: Journal of Solid State Chemistry, 1996, 127[1], 31-9